Material as used herein refers to and includes any form of information material such as, for example, video material, audio material and material for conveying data.
A watermark is a term generally used to describe data or information, which has been embedded in material in some way. A watermark may be imperceptible or perceptible in the material.
A watermark may be used for various purposes. It is known to use watermarks for the purpose of protecting the material against, or trace, infringement of the intellectual property rights of the owner(s) of the material. For example, a watermark may identify the owner of the material. The owner is thereby provided with a facility for proving unauthorised copying of the material. A system for introducing and detecting a watermark embedded in material can therefore provide a facility for copyright protection, so that the copyright in the material can be asserted.
There are generally three statistics which are used to measure the performance of copyright protection systems. These are:
1. False positive: This is the probability of deciding that a part of the material is watermarked, even though it is actually un-watermarked. For video material the European Broadcasting Union (EBU) requires the probability of a false positive to be at most 10−8.
2. False negative: This is the probability of deciding that a part of the material is not watermarked, even though it is actually watermarked. The EBU requires the probability of a false negative to be at most 0.05.
3. Error free payload: This is the probability of finishing with an error free payload (after error-correction) if the watermark has been detected. The EBU requires the probability of having errors in the decoded payload to be at most 10−8.
International patent application number WO 99/12347 discloses an apparatus for detecting a watermark embedded in material. The apparatus is provided with a copy of the watermark to be detected. The apparatus correlates the copy of the watermark with respect to data recovered from the material. From the correlation the watermark is declared as being present or absent.